As an important characteristic and a key technology in a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) cellular communications system, a Device-to-Device (D2D) communication technology has gradually become a research focus in a global wireless communication industry in recent years, and is highly concerned and widely studied in academic and industrial circles of wireless communication. D2D communication has the following advantages: (1) a rate of data transmission between User Equipments (UE) and a capability of information exchange between the UEs are effectively improved; (2) required radio resources are reduced and resource utilization is improved; (3) a communication delay of data exchange between UEs is effectively shortened.
D2D communication means that UEs may directly exchange information and transmit wireless data with each other by using a wireless communication link. This is different from communication in a conventional cellular network in which wireless communication between different UEs needs to be implemented by means of forwarding performed by an evolved NodeB (eNodeB). In addition, UEs outside coverage of an LTE network can also use the D2D communication technology to perform wireless communication with each other. As shown in FIG. 1A, it can be learned from FIG. 1A that UE 1 and UE 2 in network coverage can implement D2D communication, and that UE 3 and UE 4 outside the network coverage can also implement D2D communication.
A D2D communication procedure is shown in FIG. 1B. Specific steps are as follows:
Step 1: UE1 obtains an SL grant (Sidelink Grant, D2D sidelink resource grant), where the SL grant is used to indicate an available D2D communication resource in a D2D communication resource pool available to the UE1, and an available period of the D2D communication resource is one Sidelink Control (SC) period.
Step 2: In one SC period, the UE1 uses an available SC resource in the D2D communication resource pool to send Sidelink Control Information (SCI).
The SCI is used to indicate a time-frequency location of a D2D data resource allocated in step 1, so that receive end UE 2 can determine, by decoding the received SCI, a location of a data resource used by the UE1 to perform D2D data transmission.
Step 3: In one SC period, UE2 receives and decodes the SCI, and determines, according to the SCI, a location of a D2D data resource used by the UE1 to send D2D communication data.
Step 4: The UE1 performs D2D communication by using the D2D data resource, to transmit the D2D communication data.
Step 5: The UE2 receives, according to the location of the D2D data resource determined in step 3, the D2D communication data sent by the UE1.
Currently, in a D2D communication process, an available period of a D2D communication resource allocated each time is only one SC period. In this case, in each SC period, a transmit end needs to redetermine a D2D communication resource, and a receive end also needs to redetermine the D2D communication resource. Therefore, D2D communication efficiency is relatively low.